1. Field of the Invention
The present invention is in the field of joint repair surgery, such as reconstruction of the anterior cruciate ligament (ACL). More particularly, the invention is in the field of tensioning devices for conditioning and pre-tensioning multiple tissue grafts used in joint repair procedures. The invention is able to independently condition and pre-tension each tissue graft individually.
2. Description of the Related Art
Recent studies have added to the understanding of graft tension by demonstrating that unequal tension in the individual strands of the tissue graft can result in significant losses in total graft strength and stiffness. Unequal conditioning of each of a multiple of tissue grafts, can lead to uneven loads being borne by each individual graft. Regardless of the causes for unequal application of material stress to each of the individual tissue grafts, the “tighter” graft (or graft with higher material stress) will reach the failure point first, thereby causing a lower load to failure for the composite graft.
While much of the focus has been directed to the issue of under tensioning, which typically results in knees that are less stable than normal, application of too much tension may in theory also have an adverse effect by constraining the joints or causing increased pressure on articular surfaces.
There are several ligament tensioning devices presently available on the market. Additionally, U.S. Pat. No. 6,679,889 to West entitled “Apparatus and methods for independently conditioning and pretensioning a plurality of ligament grafts during joint repair surgery” (#889) which is herein incorporated in its entirety. A predetermined amount of stress is applied to the tissue grafts in order to provide a reconstructed joint that has a desired amount of stability and stiffness. Inadequately tensioned tissue grafts often yield a joint that is not adequately stable or a joint that is too loose and more prone to subsequent injury and possible rupture of the tissue grafts. However, unless each strand of a multiple strand graft bears approximately the same magnitude of material stress, the strand that initially bears the highest material stress will reach the failure point and rupture first when the joint is subjected to high stress. Subsequently, the graft initially bearing less material stress will then bear all the stress and be more prone to failure since it will be acting on its own to hold the joint together.
Embodiments of the present tensioning assembly provide features that address shortcomings present in tensioning assemblies known on the market today.